Studies are proposed to execute a covergent, enantioselective synthesis of several members of the class of milbemycins and avermectins. The milbemycins are potent antimicrobial agents and the avermectins show exceptional anthelminthic properties with low mammalian toxicity. Additional studies are outlined to develop an enantioselective anti aldol condensation which could have wide application in the synthesis of bio-active natural products. Applications to the milbemycin-avermectin problem are discussed as well as synthetic approaches to nonactin, an antibiotic ionophore, the Prelog Djerassi lactone, and the tumor promoting neurotoxin, aplysiatoxin.